
In a pan over medium heat, heat about 1/2 cup oil. Add garlic and cook, stirring regularly, until golden brown and crisp. Using a slotted spoon, remove from pan and drain on paper towels. Reserve oil.
Season fish with salt and pepper to taste. Lightly dredge in flour to fully coat.
Add to the pan (with garlic oil) in a single layer and cook, turning as needed until nicely golden crisp, and cooked through. Remove from pan and keep warm.
In a small bowl, combine lemon juice, soy sauce, oyster sauce, brown sugar, and water. Stir until blended and set aside.
In a pan over medium heat, heat about 1 tablespoon butter.
Add the sauce mixture and bring to a simmer. Continue to cook until slightly reduced.
Arrange fried bangus on a heated sizzling plate. Drizzle with the sauce and garnish with onion rings and toasted garlic. Serve hot.